The aim of the proposal is monitoring of gap junction channel activity. A preparation has been developed which allows exposure of cytoplasmic surfaces of membranes that contain gap junctions. The septal membranes of the extracellular clamp methods are used to allow monitoring of gap junction channels. The specific aims are: (1) Use the patch clamp to record single channels from an exposed cytoplasmic surface when the exposed membrane is known to contain gap junctions. (2) Determine if channel behavior is consistent with known properties of gap junctions. (3) Study the ultrastructure of the dissected preparation to determine if there are any morphological changes in gap junctions. (4) Determine the effects of H+, Ca++ and other agents on channel activity. (5) Study the effects of solvent exchange on the conductive properties of the channels. (6) Determine the selectivity sequence. (7) Use the double voltage clamp as a means of measuring macroscopic behavior.